Re: [PATCH] arm64/numa: Add more vetting in numa_set_distance()

John Garry
2018-10-29T12:14:26Z

On 29/10/2018 11:25, Will Deacon wrote:
> Hi John,
>

Hi Will,

> On Fri, Oct 26, 2018 at 09:57:47PM +0800, John Garry wrote:
>> Currently it is acceptable to set the distance between 2 separate nodes to
>> LOCAL_DISTANCE.
>>
>> Reject this as it is invalid.
>>
>> This change avoids a crash reported in [1].
>>
>> [1] https://www.spinics.net/lists/arm-kernel/msg683304.html
>>
>> Signed-off-by: John Garry <john.garry@huawei.com>
>>
>> diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
>> index 146c04c..6092e3d 100644
>> --- a/arch/arm64/mm/numa.c
>> +++ b/arch/arm64/mm/numa.c
>> @@ -335,7 +335,8 @@ void __init numa_set_distance(int from, int to, int distance)
>> }
>>
>> if ((u8)distance != distance ||
>> - (from == to && distance != LOCAL_DISTANCE)) {
>> + (from == to && distance != LOCAL_DISTANCE) ||
>> + (from != to && distance == LOCAL_DISTANCE)) {
>
> The current code here is more-or-less lifted from the x86 implementation
> of numa_set_distance().

Right, I did notice this. I didn't think that x86 folks would be so
concerned since they generally only use ACPI, and the ACPI code already
validates these distances in drivers/acpi/numa.c: slit_valid() [unlike
OF code].

I think we should either factor out the sanity check
> into a core helper or make the core code robust to these funny configurations.

OK, so to me it would make sense to factor out a sanity check into a
core helper.

Cheers,
John

>
> Will
>
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